CN102193176B

CN102193176B - Zoom lens, imaging device and information device

Info

Publication number: CN102193176B
Application number: CN201110062478.3A
Authority: CN
Inventors: 须藤芳文
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2010-03-12
Filing date: 2011-03-11
Publication date: 2014-10-01
Anticipated expiration: 2031-03-11
Also published as: US20110222169A1; US8405917B2; EP2365371B1; EP2365371A1; JP5590444B2; JP2011191353A; CN102193176A

Abstract

The invention relates to a zoom lens, an imaging device and an information device. The zoom lens includes, in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, the second lens group including, in order from the object side, a first negative lens and a cemented lens including a second negative lens having a convex shape on the object side and a positive lens, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and an aperture stop arranged between the second lens group and the third lens group, wherein when changing a magnification from a short focal end to a telephoto end, an interval between the first lens group and the second lens group is increased, an interval between the second lens group and the third lens group is decreased, an interval between the third lens group and the fourth lens group is increased, and the first lens group and the third lens group are moved to be located closer to the object side at the long focal end than the short focal end.

Description

Zoom lens, imaging apparatus, and information apparatus

Technical Field

The present invention relates to a zoom lens having a zoom function of changing an angle of field (field angle) by changing a focal length, and more particularly to a zoom lens suitable for a digital camera, a video camera, or the like which obtains digital image data of a subject (subject) by using an imaging element, an imaging apparatus using such a zoom lens as an imaging optical system, and an information apparatus such as a personal digital assistant having such an imaging function.

Background

There is a significant growth in the digital camera market, and users have a wide variety of needs for digital cameras. In particular, users always desire high-quality photo technology and size reduction technology, which are major demands of users of digital cameras. For this reason, a zoom lens used as a photographing lens also requires high-quality photograph technology and size reduction technology.

For the size reduction technique, first, it is necessary to reduce the overall length of the lens used (the distance from the most object side lens surface to the imaging plane), and it is also important to reduce the overall length in the collapsed state (collapsed state) by reducing the thickness of each lens group. For high performance technologies, the entire zoom range requires a resolution corresponding to an imaging element having at least 1 million to 1 thousand 5 million pixels.

Further, many users require a wider opening angle of the photographing lens, and the half opening angle of the zoom lens at the short focal end is preferably 38 degrees or more. In the case of a silver salt camera using a silver salt film (i.e., lycra film) having a width of 35mm, a half aperture angle of 38 degrees corresponds to a focal length of 28 mm.

In addition, high magnification is also required. The zoom lens having a focal length corresponding to about 28 to 200mm in a 35mm silver salt camera conversion (about 7.1 times) is capable of all ordinary photographing.

As a zoom lens for a digital camera, various types of zoom lenses can be used. As a zoom lens suitable for high performance, there is a zoom lens including, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, in which, when changing magnification from a short focal end to a long focal end, an interval between the first lens group and the second lens group increases, an interval between the second lens group and the third lens group decreases, and an interval between the third lens group and the fourth lens group changes.

This type of zoom lens includes, for example, a zoom lens in which the first lens group is fixed when changing magnification, and a zoom lens in which the first lens group reciprocates in an arc having a convex shape on the image side when changing magnification. In this type, if a large displacement of the second lens group mainly sharing the magnification function is ensured, the aperture stop arranged around the third lens group is separated from the first lens group even when the zoom lens is at the short focal end. Accordingly, for a wide-angle high magnification zoom lens, the size of the first lens group increases. Therefore, in order to realize a wide angle, a high magnification, and a small zoom lens, it is preferable that the first lens group is moved to be positioned closer to the object side at the telephoto end than at the short focal end. By reducing the entire length of the lens at the short focal end compared to that at the long focal end, the first lens group is prevented from increasing in size, and a sufficient wide angle can be achieved.

Since the second lens group is configured as an inverter having a main magnification function, the configuration of the second lens group is very important. As known second lens groups, for example, a second lens group including three lenses, in order from the object side, a negative lens having a large curved surface on the image side, a negative lens having a concave surface on the object side, and a positive lens having a convex surface on the object side, which are arranged in order from the object side, is described in japanese patent application nos. 2008-145501, 2006-23531, and 3328001.

Further, as a known second lens group, a second lens group including three lenses of a negative lens having a large curved surface on the image side, a negative lens having a convex surface on the object side, and a positive lens having a convex surface on the object side, which are arranged in order from the object side, is described in japanese patent application No. 2009-198798.

However, the zoom lens described in each of Japanese patent application Nos. 2008-145501 and 2006-23531 is not a high performance zoom lens of 8 times or more. Further, the second negative lens and the positive lens from the object side in the second lens group are not joined, so that the decentering amount (eccentric amount) of these lenses increases, resulting in a decrease in resolution. On the other hand, the zoom lens described in japanese patent No.3328001 has a high magnification. However, the overall length of the lens at the telephoto end is increased, so that a small zoom lens is not realized.

Further, the zoom lens described in japanese patent application No.2009-198798 is not a high-performance zoom lens of 8 times or more. In the zoom lens, the second negative lens from the object side and the third lens in the second lens group are not joined, so that the decentering amount of these lenses increases, resulting in a decrease in resolution.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a zoom lens having a sufficiently wide angle, that is, a half aperture angle of 38 degrees or more at a short focal end, and a magnification of 8 times or more. The zoom lens also realizes a small size with a configuration of about 10 lenses and a resolution corresponding to an imaging element having 1 million to 1 thousand 5 million pixels for the entire magnification range. It is also an object of the present invention to provide an imaging apparatus and an information apparatus using such a zoom lens.

In order to achieve the above object, an embodiment of the present invention provides a zoom lens including, in order from an object side: a first lens group having a positive refractive power; a second lens group having a negative refractive power, the second lens group including, in order from an object side, a first negative lens, and a cemented lens including a second negative lens having a convex shape on the object side and a positive lens; a third lens group having positive refractive power; a fourth lens group having positive refractive power; and an aperture stop disposed between the second lens group and the third lens group. When changing magnification from a short focal end to a far focal end, an interval between the first lens group and the second lens group increases, an interval between the second lens group and the third lens group decreases, an interval between the third lens group and the fourth lens group increases, and the first lens group and the third lens group are moved to be positioned closer to the object side at the long focal end than at the short focal end, wherein the following conditional expression is satisfied, wherein an interval between the second lens group at the short focal end and the aperture stop is D2Sw, and an interval between the aperture stop at the short focal end and the third lens group is DS3 w;

0.3＜DS3w/D2Sw＜2.0。

preferably, the following conditional expression is satisfied, wherein a focal length of the first negative lens of the second lens group is f21, and a focal length of the second negative lens of the second lens group is f 22;

0.1＜f21/f22＜0.8

preferably, the following conditional expression is satisfied, in which a focal length of the first negative lens of the second lens group is f21, and a focal length of the second lens group is f 2;

0.5＜f21/f2＜1.5

preferably, the following conditional expression is satisfied, in which a thickness of the second lens group on the optical axis is D2, and a focal length of the entire lens system at the short focal end is fw;

0.7＜D2/fw＜1.3。

preferably, the positive lens of the second lens group is a positive meniscus lens having a convex surface on the object side and an aspherical lens forming an aspherical surface on the image side.

Preferably, the following conditional expression is satisfied, in which a variation in an interval between the first lens group and the second lens group when changing the magnification from the short focal end to the long focal end is X1-2, and a focal length of the second lens group is f 2;

2.0＜|×1-2/f2|＜4.0。

preferably, the following conditional expression is satisfied, wherein an effective beam diameter of an object side surface of the first negative lens of the second lens group isAnd the effective beam diameter of the object side surface of the second negative lens of the second lens group is

Embodiments of the present invention also provide an imaging apparatus including the zoom lens according to an embodiment of the present invention as an imaging optical system.

Embodiments of the present invention also provide an information apparatus including the zoom lens according to an embodiment of the present invention as an imaging optical system.

Drawings

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

Fig. 1 is a schematic diagram showing the configuration of an optical system and a zoom locus of a zoom lens system according to embodiment 1 of the first embodiment of the present invention.

Fig. 2 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 1 shown in fig. 1 at the short focal end (wide-angle end).

Fig. 3 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 1 shown in fig. 1 at an intermediate focal length.

Fig. 4 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 1 shown in fig. 1 at a telephoto end (tele end).

Fig. 5 is a schematic diagram showing the configuration of an optical system and a zoom locus of a zoom lens system according to embodiment 2 of the first embodiment of the present invention.

Fig. 6 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 2 shown in fig. 5 at the short focal end (wide-angle end).

Fig. 7 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 2 shown in fig. 5 at an intermediate focal length.

Fig. 8 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 2 shown in fig. 5 at a telephoto end (far focus end).

Fig. 9 is a schematic diagram showing the configuration of an optical system and a zoom locus of a zoom lens system according to embodiment 3 of the first embodiment of the present invention.

Fig. 10 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 3 shown in fig. 9 at the short focal end (wide-angle end).

Fig. 11 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 3 shown in fig. 9 at an intermediate focal length.

Fig. 12 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 3 shown in fig. 9 at a telephoto end (far focus end).

Fig. 13 is a schematic diagram showing the configuration of an optical system and a zoom locus of a zoom lens system according to embodiment 4 of the first embodiment of the present invention.

Fig. 14 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 4 shown in fig. 13 at the short focal end (wide-angle end).

Fig. 15 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 4 shown in fig. 13 at an intermediate focal length.

Fig. 16 is a view showing aberration curves of spherical aberration, astigmatism, distortion, and coma aberration in the zoom lens according to embodiment 4 shown in fig. 13 at a telephoto end (far focus end).

Fig. 17 is a perspective view showing an appearance of a digital camera as an imaging apparatus seen from an object side according to the second embodiment of the present invention.

Fig. 18 is a perspective view showing an appearance of the digital camera in fig. 17 as seen from the photographer side.

Fig. 19 is a block diagram showing a functional configuration of the digital camera in fig. 17.

Fig. 20 is a diagram showing an imaging domain describing electrical correction of distortion by image processing according to an embodiment of the present invention.

Detailed Description

Hereinafter, details of a zoom lens, an imaging apparatus, and an information apparatus according to embodiments of the present invention are described with reference to the drawings.

A zoom lens according to a first embodiment of the present invention includes, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, wherein when changing magnification from a short focal end (wide angle end) to a long focal end (telephoto end), an interval between the first lens group and the second lens group increases, an interval between the second lens group and the third lens group decreases, an interval between the third lens group and the fourth lens group increases, and the first lens group and the third lens group are moved to be positioned closer to the object side at the long focal end than at the short focal end.

First, a first feature of a zoom lens according to an embodiment of the present invention is that an aperture stop is disposed between a second lens group and a third lens group, and the second lens group is made to include, in order from an object side, a first negative lens, a second negative lens having a convex shape on the object side, and a positive lens, the second negative lens and the positive lens being closely attached to each other to form a cemented lens (centered lenses).

Next, a second feature of the zoom lens according to the embodiment of the present invention is that the following conditional expression is satisfied,

0.1＜f21/f22＜0.8

where f21 is the focal length of the first negative lens (L21) of the second lens group, and f22 is the focal length of the second negative lens (L22) of the second lens group.

A third feature of the zoom lens according to the embodiment of the present invention is that the following conditional expression is satisfied,

0.5＜f21/f2＜1.5

where f21 is the focal length of the first negative lens (L21) of the second lens group, and f2 is the focal length of the entire second lens group.

A fourth feature of the zoom lens according to the embodiment of the present invention is that the following conditional expression is satisfied,

0.7＜D2/fw＜1.3

where D2 is the thickness of the second lens group on the optical axis, and fw is the focal length at the short focal end.

A fifth feature of the zoom lens according to the embodiment of the present invention is that the following conditional expression is satisfied,

0.3＜DS3w/D2Sw＜2.0

where D2Sw is the interval between the second lens group and the aperture stop at the short focal end, and DS3w is the interval between the aperture stop and the third lens group at the short focal end.

A sixth feature of the zoom lens according to the embodiment of the present invention is that the image-side surface of the positive lens of the second lens group has a convex shape on the object side (i.e., the image-side surface of the positive lens of the second lens group is a concave surface) and a spherical surface.

A seventh feature of the zoom lens according to the embodiment of the present invention is that the following conditional expression is satisfied,

2.0＜|×1-2/f2|＜4.0

where X1-2 is a change in the interval between the first lens group and the second lens group when changing magnification from the short focal end to the long focal end, and f2 is the focal length of the entire second lens group.

An eighth feature of the zoom lens according to the embodiment of the present invention is that the following conditional expression is satisfied,

wherein,is an object of the first negative lens (L21) of the second lens groupThe effective beam diameter of the side surface,is an effective beam diameter of an object side surface of the second negative lens (L22) of the second lens group.

In a zoom lens including four lens groups of positive, negative, positive, and positive, the second lens group generally has a main magnification function as a variator. When changing magnification from the short focal end to the long focal end, the first lens group is moved significantly toward the object side, so that the height of the light beam passing through the first lens group at the short focal end is lowered. Accordingly, an increase in size of the first lens group is prevented in a wider-angle zoom lens, and a large interval between the first lens group and the second lens group is secured at a telephoto end to achieve a long focal length.

When changing magnification from the short focal end to the long focal end, the interval between the first lens group and the second lens group increases, and the interval between the second lens group and the third lens group decreases, so that the magnification (absolute value) of both the second lens group and the third lens group increases, and thus the magnification function is shared by the second lens group and the third lens group.

In conventional optical design, the negative lens on the most object side in the second lens group has only a certain amount of refractive power. For this reason, in order to reduce distortion of the short focal end, the object side surface of the second negative lens (L22) in the second lens group from the object side has a concave shape to increase the incident angle with respect to the surface of the off-axis light beam, thereby obtaining a degree of freedom of correction of off-axis aberration of the short focal end. However, by correcting distortion of an image by image processing, a design that accepts distortion can be obtained.

Therefore, in the zoom lens according to the embodiment of the present invention, the second lens group includes, in order from the object side, the negative lens (L21) and the cemented lens in which the convex-shaped negative lens (L22) and the positive lens (L23) on the object side are closely attached to each other.

By accepting distortion of the short focal end, the most object side negative lens (L21) in the second lens group has a large refractive power, so that off-axis aberration in the second lens group can be sufficiently corrected. Therefore, by using the convex surface of the object side surface of the second negative lens (L22) from the object side in the second lens group, the aberration generated in the surface can be reduced, and the influence of eccentricity (eccentricity) or the like can be reduced. In addition, by combining the negative lens (L22) and the positive lens (L23) having a large refractive power at the short focal end, the influence of the eccentricity of the negative lens (L22) with respect to the positive lens (L23) can be sufficiently suppressed.

In order to control the influence of eccentricity and the like at a high level, it is desirable to satisfy the following conditional expression (1).

0.1＜f21/f22＜0.8

In the above-described conditional expression (1), if the value is out of the range of the upper limit value and the lower limit value, the first negative lens (L21) of the second lens group or the second negative lens (L22) of the second lens group has a strong refractive power, and a lens having a strong refractive power generates large aberration, so that it is difficult to correct aberration of the entire zoom range. It is also difficult to control the influence of eccentricity of a lens having a strong refractive power.

More preferably, the following conditional expression (1') is satisfied.

0.2＜f21/f22＜0.7

In order to control the influence of eccentricity and the like at a high level, the following conditional expression (2) is preferably satisfied.

0.5＜f21/f2＜1.5

In the above conditional expression (2), if the value exceeds the upper limit value, the height of the off-axis light beam passing through the second lens group at the short focal end increases, so that it is difficult to correct the off-axis aberration at the short focal end. If the value is lower than the lower limit value, the aberration generated at the image-side surface of the negative lens (L21) becomes too large, making it difficult to correct the aberration of the entire zoom range. The influence of the eccentricity of the image-side surface of the negative lens (L21) also increases in image quality.

More preferably, the following conditional expression (2') is satisfied.

0.7＜f21/f2＜1.2

In order to further improve the performance of the zoom lens and reduce the size of the zoom lens, it is preferable that the following conditional expression (3) is satisfied.

0.7＜D2/fw＜1.3

Where D2 is the thickness of the second lens group on the optical axis, and fw is the focal length of the entire lens system at the short focal end.

In the above conditional expression (3), if the value exceeds the upper limit value, the thickness of the second lens group on the optical axis increases, and a space for changing the magnification of the second lens group decreases, so that it is difficult to correct aberrations over the entire zoom range. If the value is lower than the lower limit value, a space constituting the second lens group becomes too small, so that it becomes difficult to correct aberrations in the second lens group.

More preferably, the following conditional expression (3') is satisfied.

0.8＜D2/fw＜1.2

In order to further improve the performance of the zoom lens and reduce the size of the zoom lens, it is preferable that the following conditional expression (4) is satisfied.

0.3＜DS3w/D2Sw＜2.0

If the value is lower than the lower limit value, the interval between the second lens group and the aperture stop increases, and the height of the off-axis light beam passing through the second lens group at the short focal end becomes too high, so that it becomes difficult to correct off-axis aberration in the second lens group, resulting in an increase in the size of the second lens group. If the value exceeds the upper limit value, the interval between the third lens group and the aperture stop increases, and the height of the off-axis light beam passing through the third lens group at the short focal end becomes too high, so that it becomes difficult to correct aberrations in the third lens group, resulting in an increase in the size of the third lens group.

More preferably, the following conditional expression (4') is satisfied.

0.6＜DS3w/D2Sw＜1.5

In addition, it is preferable to configure the zoom lens such that when the magnification is changed from the short focal end to the long focal end, the interval between the aperture stop and the third lens group decreases.

In order to further improve the performance of the zoom lens, it is preferable that the image-side surface of the positive lens of the second lens group has a convex surface on the object side, and is a spherical surface. If the shape of the spherical surface is formed so that the negative refractive power decreases, the aberration in the second lens group can be controlled.

The performance can be further improved if the positive lens of the second lens group satisfies the following conditional expression.

2.2＞Nd_23＞1.95

25＞vd_23＞15

Where Nd _23 is a refractive index of a d-line of the positive lens (L23) of the second lens group, and ν d _23 is an abbe number according to the d-line of the positive lens (L23) of the second lens group.

In order to further improve the performance, the following conditional expression (5) is preferably satisfied.

2·0＜|×1-2/f2|＜4.0

In the above conditional expression (5), if the value exceeds the upper limit value, the magnification of the second lens group becomes too large, and the magnification effect of the third lens group cannot be obtained, so that it is difficult to correct aberrations over the entire zoom range. If the value is lower than the lower limit value, the magnification of the second lens group becomes too small, it becomes necessary for the third lens group to have a large magnification, so that it becomes difficult to correct aberrations as the entire zoom range.

More preferably, the following conditional expression (5') is satisfied.

2.5＜|×1-2/f2|＜3.5

In order to improve performance and control the influence of eccentricity and the like, the following conditional expression (6) is preferably satisfied.

Wherein,is an effective beam diameter of an object side surface of the negative lens (L21) of the second lens group, andis an effective beam diameter of the object side surface of the negative lens (L22) of the second lens group.

In the above conditional expression (6), if the value exceeds the upper limit value, the diameter of the off-axis light beam passing through the second lens group at the short focal end increases, so that it is difficult to correct the off-axis aberration at the short focal end. If the value is smaller than the lower limit value, the aberration generated on the image side of the negative lens (L21) becomes too large, making it difficult to correct the aberration of the entire zoom range. The influence of the eccentricity of the image-side surface of the negative lens (L21) also increases in image quality.

More preferably, the following conditional expression (6') is satisfied.

In order to reduce the size of the zoom lens and further improve the performance of the zoom lens, it is preferable that the following conditional expression (7) is satisfied.

-1.5＜f2/fw＜-0.8

In the above conditional expression (7), if the value exceeds the upper limit value, the refractive power of the second lens group is too strong, so that it is difficult to correct aberrations in the second lens group. If the number of lenses is further increased in the second lens group, the size of the second lens group increases. If the value is lower than the lower limit value, the refractive power of the second lens group is weak and the contribution to the magnification of the second lens group is reduced, so that the contribution to the magnification of the third lens group needs to be improved, and it is difficult to correct aberrations in the third lens group.

In order to further improve the performance of the zoom lens and reduce the size of the zoom lens, it is preferable that the following conditional expression (8) is satisfied.

0.8＜TLt/ft＜1.5

Where TLt is the overall length of the short focal end and ft is the focal length of the long focal end.

In the above-described conditional expression (8), if the value exceeds the upper limit value, the entire length of the tele end increases, so that the entire length of the tele end becomes dominant with respect to the thickness of the camera. If the value is lower than the lower limit value, a sufficient entire length of the tele end cannot be ensured, so that it is difficult to correct the aberration of the tele end.

By setting the opening diameter of the aperture stop to be larger at the telephoto end than at the short-focus end, the change in the F-number when changing the magnification can be reduced. When the light amount reaching the imaging plane needs to be reduced, the size of the aperture stop may be reduced, but it is preferable to reduce the light amount by inserting an ND filter or the like without significantly changing the size of the aperture stop, because the resolution reduction caused by the refraction phenomenon can be prevented.

The focusing operation can be performed by expanding the entire system, but is preferably performed only by the movement of the fourth lens group.

The basic configuration of the zoom lens according to the first embodiment of the present invention is described above. Hereinafter, details of the zoom lens according to the present embodiment are described in the embodiments described below with reference to fig. 1 to 16, based on specific numerical examples.

Next, a digital camera as an imaging apparatus according to a second embodiment of the present invention, which uses a zoom lens according to a first embodiment of the present invention as an imaging optical system, will be described with reference to fig. 17 to 19. Fig. 17 is a perspective view showing an appearance of the digital camera seen from a front side which is a subject side, i.e., an object side. Fig. 18 is a perspective view showing an appearance of the digital camera seen from a rear side which is a photographer side. Fig. 19 is a block diagram showing a functional configuration of the digital camera. In addition, the imaging apparatus is described using a digital camera as an example, but the zoom lens according to the embodiment of the present invention may be applied to a silver salt film camera using a silver salt film as an image recording medium. In addition, information apparatuses having a camera function, such as portable digital assistants, e.g., PDAs (personal data assistants), and cellular phones, are widely used. Although slightly different in appearance, this information apparatus has a function and a configuration substantially similar to those of a digital camera. As an imaging optical system in such an information apparatus, a zoom lens according to an embodiment of the present invention can be used.

As shown in fig. 17 and 18, the digital camera includes a photographing lens 101, an optical viewfinder 102, a strobe (flash) 103, a shutter button 104, a camera body 105, a power switch 106, a liquid crystal monitor 107, an operation button 108, a memory card slot 109, and a zoom switch 110. As shown in fig. 19, the digital camera includes a Central Processing Unit (CPU) 111, an image processor 112, a light receiving element 113, a signal processor 114, a semiconductor memory 115, and a communication card 116.

The digital camera includes a photographing lens 101 as an imaging optical system and a light receiving element 113 as an image sensor such as a CMOS (complementary metal oxide semiconductor) and a CCD (charge coupled device). The light receiving element 113 reads an optical image of an object (subject) focused by the photographing lens 101. As this photographing lens 103, a zoom lens according to the first embodiment of the present invention is used.

The single processor 114 controlled by the CPU111 processes the output of the light receiving element 113 and converts the output into digital image information. More specifically, the digital camera includes a unit that converts a photographed image (subject image) into digital image information. This unit is constituted by a light receiving element 113, a signal processor 114, and a CPU111 and the like which control these units.

After predetermined image processing is performed on the image information digitized by the signal processor 114 in an image processor 112 controlled by the CPU111, the image information is recorded in a semiconductor memory 115 such as a nonvolatile memory. In this case, the semiconductor memory 115 may be a memory card loaded into the memory card slot 109, and may be a semiconductor memory (on-board memory) built in the camera body. The liquid crystal monitor 107 can display an image at the time of shooting, and can display an image recorded in the semiconductor memory 115. The image recorded in the semiconductor memory 115 may be transmitted to the outside via a communication card 116 or the like loaded into a communication card slot, not shown.

The subject-side surface of the photographing lens 101 is covered by a lens barrier, not shown, in a hand-held state. If the user turns on the switch by operating the power switch 106, the lens barrier is opened and the object surface is exposed. In this case, in a lens barrel (lens barrel) of the photographing lens 101, an optical system of each group constituting the zoom lens is arranged at, for example, a short focal end (wide-angle end), a position of the optical system of each group is changed by operating the zoom switch 110, and an operation of changing a magnification to a long focal end (far focal end) via an intermediate focal length can be performed. In addition, it is preferable that the optical system of the optical viewfinder 102 changes the magnification in conjunction with the change of the opening angle of the photographing lens 101.

In many cases, focusing is performed by half-pressing the shutter button 104. Focusing in the zoom lens according to the embodiment of the present invention may be performed by moving a part of groups of optical systems constituting a plurality of groups of the zoom lens and moving the light receiver. If the shutter button 104 is fully pressed, shooting is performed, followed by the above-described processing.

When an image recorded in the semiconductor memory 115 is displayed on the liquid crystal monitor 107 and transmitted to the outside via the communication card 116 or the like, the operation buttons 108 are operated as specified. The semiconductor memory 115, the communication card 116, and the like are loaded into dedicated slots such as the memory card slot 109 and the communication card slot or general slots.

As described above, the photographing lens 101 configured using the zoom lens shown in the first embodiment can be used on the above-described digital camera (imaging apparatus) and information apparatus as an imaging optical system. Therefore, a high-quality and compact digital camera (imaging device) or information device using a light-receiving element having 1 million to 1 thousand 5 million pixels or more can be realized.

[ example 1]

Next, specific embodiments of the zoom lens according to the first embodiment of the present invention described above will be described. Embodiments 1 to 4 are embodiments according to specific configurations of specific numerical examples of zoom lenses according to embodiments of the present invention. In embodiments 1 to 4, the configuration and specific numerical example of the zoom lens are shown.

In each of embodiments 1 to 4, the optical element having the parallel plate arranged on the image side of the fourth lens group employs, for example, various optical filters such as an optical low-pass filter and an infrared cut filter and a cover glass (shield glass) of a light receiving element such as a CMOS image sensor. In this case, it is referred to as a filter or the like (FM).

The material of the lens in each of the zoom lenses in embodiments 1 to 4 is optical glass, except that the material of the positive lens of the fourth lens group in each of the zoom lenses in embodiments 1 to 4 is optical plastic.

In each of embodiments 1 to 4, both of an object-most side surface and an image-most side surface (most image side) of the second lens group, a surface of an image-most side lens of the third lens group, and an object side surface of the fourth lens group are aspherical surfaces, respectively. In addition, the aspherical surfaces in examples 1 to 4 are described as surfaces in which each lens surface is directly manufactured as an aspherical surface as in the case of casting an aspherical lens. However, the aspherical lens may be constituted by a hybrid aspherical surface or the like, which is obtained by providing a resin film forming the aspherical surface on the surface of the spherical lens.

The aberrations in examples 1-4 were well corrected. The zoom lenses in embodiments 1 to 4 may correspond to the zoom lens having light receiving elements of 1 million to 1 thousand 5 million pixels or more. By constituting the zoom lens according to the embodiment of the present invention, it is apparent from embodiments 1 to 4 that better image performance can be obtained while sufficiently reducing the size of the zoom lens.

In addition, in the zoom lenses of embodiments 1 to 4, as described above, distortion is corrected by image processing. That is, in the zoom lenses of embodiments 1 to 4, as shown in fig. 20, barrel distortion such as an imaging region WF is generated on the light receiving surface TF of the rectangular light receiving element at the short focal end. In addition, in fig. 20, TF is an imaging area of the light receiving element (an imaging area of the intermediate focal length and the telephoto end (the far focal end)), and WF is an imaging area of the short focal end (the wide-angle end). On the other hand, the generation of distortion is controlled at the intermediate focal length, a state close to the intermediate focal length, and the telephoto end. To electrically correct for distortion, the effective imaging area is set to barrel (WF) at the short focal length and rectangular (TF) at the intermediate and long focal lengths. An image of an effective imaging area (WF) at a short focal end is converted into rectangular image information with reduced distortion by image processing. Therefore, in each of embodiments 1 to 4, the image height of the short focal end is set to be smaller than the image height of the intermediate focal length and the image height of the long focal end.

In addition, the meanings of the reference symbols in the following examples 1 to 4 are as follows.

f: focal length of entire system of zoom lens

F: f value (F number)

ω: half opening angle

R: radius of curvature

D: surface spacing

Nd: refractive index

V d: abbe number

Effective beam diameter

K: conic constant of non-spherical surface

A₄: fourth order aspherical surface coefficient

A₆: coefficient of six-order aspheric surface

A₈: coefficient of aspheric surface of order eight

A₁₀: coefficient of ten-order aspheric surface

An aspherical surface is defined by the following equation 1, where C is the inverse of the paraxial radius of curvature (paraxial curvature), H is the height from the optical axis, and A_2iIs a displacement from the surface vertex in the optical axis direction.

[ equation 1]

Fig. 1 is a schematic view showing the configuration of an optical system of a zoom lens according to embodiment 1 of the first embodiment of the present invention and a zoom locus from a short focal end (wide-angle end) to a long focal end (telephoto end) via a predetermined intermediate focal length; (a) a cross-sectional view along the optical axis of a short focal end (Wide) is shown; (b) a cross-sectional view along the optical axis showing a focal length between a short focal end and an intermediate focal length (Wide-Mean); (c) a cross-sectional view along the optical axis showing an intermediate focal length (Mean); (d) a cross-sectional view along the optical axis showing the focal length between the intermediate focal length and the Tele end (intermediate-Tele); (e) a cross-sectional view along the optical axis of the Tele end (Tele) is shown. In addition, in fig. 1 showing the lens group arrangement of embodiment 1, the left side in the figure is the object (subject) side.

The zoom lens shown in fig. 1 includes, in order along the optical axis from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and an aperture stop AD between the second lens group G2 and the third lens group G3. The first lens group includes a first lens L11, a second lens L12, and a third lens L13. The second lens group G2 includes a first lens L21, a second lens L22, and a third lens L23. The third lens group G3 includes a first lens L31, a second lens L32, and a third lens L33. The fourth lens group G4 includes a single lens L40.

The first-fourth lens groups G1-G4 are supported by a support frame common to each of the lens groups, respectively, and work together for each lens group upon zooming. The aperture stop AD works independently of each group. In fig. 1, the surface number of each optical surface is shown. In addition, reference numerals in fig. 1 are used for each embodiment to avoid complicating the description due to the increase in the number of the reference numerals. For this reason, in the case where reference numerals common to numerals in the drawings of the other embodiment are applied, these are not always configurations common to the other embodiment.

When changing magnification from the short focal end (wide-angle end) to the long focal end (telephoto end), all of the first-fourth lens groups G1-G4 are moved such that the interval between the first lens group G1 and the second lens group G2 increases, the interval between the second lens group G2 and the third lens group G3 decreases, the interval between the third lens group G3 and the fourth lens group G4 increases, and the first lens group G1 and the third lens group G3 are moved to be positioned closer to the object side at the long focal end than at the short focal end.

The first lens group G1 includes, in order from the object side, a first lens (negative lens) L11 of a negative meniscus lens having a convex surface on the object side, a second lens (first positive lens) L12 of a double convex positive lens having a strong convex surface on the object side, and a third lens (third positive lens) L13 of a positive meniscus lens having a convex surface on the object side. The two lenses of the first lens L11 and the second lens L12 are closely attached to each other to form a cemented lens having two lenses.

The second lens group G2 includes, in order from the object side: a first lens (first negative lens) L21 which is a negative meniscus lens having a convex surface on the object side and an aspherical lens forming an aspherical surface on the object side; a second lens (second negative lens) L22 of a negative meniscus lens having a convex surface on the object side; and a third lens (positive lens) L23 which is a positive meniscus lens having a convex surface on the object side and an aspherical lens forming an aspherical surface on the image side. The two lenses of the second lens L22 and the third lens L23 are closely attached to each other to form a cemented lens of the two lenses.

The aperture stop AD is disposed between the second lens group G2 and the third lens group G3. The third lens group G3 includes, in order from the object side: a first lens (first positive lens) L31 which is a biconvex positive lens having a strong convex surface on the object side and an aspherical lens forming aspherical surfaces on both surfaces; a second lens (second positive lens) L32 of a double convex positive lens having a strong convex surface on the object side; and a third lens (negative lens) L33 of a double concave negative lens having a strong concave surface on the image side. The two lenses of the second lens L32 and the third lens L33 are closely attached to each other to form a cemented lens of the two lenses.

The fourth lens group G4 includes a single positive lens L40, and the lens L40 is a biconvex positive lens having a strong convex surface on the object side and an aspherical lens having an aspherical surface on the object side.

In this case, as shown in fig. 1, when changing the magnification from the short focal end (wide angle end) to the long focal end (telephoto end), the first lens group G1 monotonously moves from the image side to the object side, the second lens group G2 moves to the image side to describe a convex locus, and the third lens group G3 moves from the image side to the object side, from the object side to the image side, and again from the image side to the object side, the fourth lens group G4 moves to the object side to describe a convex locus.

The optical characteristics of each optical element in example 1 are as shown in table 1 below.

[ Table 1]

In table 1, "+" denotes a non-spherical surface, "HOYA" and "OHARA" denote the names of glass manufacturers HOYA inc. This is the same in another embodiment.

That is, in table 1, each of the sixth, tenth, twelfth, thirteenth, and seventeenth surfaces to which ". sup." is applied is an aspherical surface, and the parameters of each of the aspherical surfaces in equation 1 are as shown in table 2 below.

[ Table 2]

Coefficient of non-spherical surface

	K	A4	A6	A8	A10
						6	0	-3.59577E-04	2.88790E-06	1.05189E-07	-2.41047E-09
10	0	-7.38687E-04	-4.1216.E-06	5.00682E-07	-9.07816E-08
						12	0	-6.5.523E-04	2.94728E-05	-2.54075E-06	1.16148E-07
13	0	1.73404E-04	4.00476E-05	-3.54538E-06	1.57333E-07
						17	0	-5.77707E-05	4.41283E-06	-1.53886E-07	2.60428E-09

In embodiment 1, as zooming proceeds, the focal length F, F value F, variation interval DA between the first and second lens groups G1, G2, variation interval DB between the second lens group G2 and the aperture stop AD, variation interval DC between the aperture stop AD and the third lens group G3, variation interval DD between the third and fourth lens groups G3, G4, and variation interval DE between the fourth lens group G4 and the filter FM, etc. of the entire optical system are changed as shown in table 3 below.

[ Table 3]

The aperture stop at the tele end has an opening diameter ofThe image height Y' = 4.1. Referring to fig. 20, as described above, in order to correct distortion by image processing, the imaging region of the long focus end (intermediate focal length) substantially conforms to the imaging region of the light receiving element to obtain a rectangular imaging region, and distortion is generated at the short focus (wide angle) end so that the imaging region of the short focus end becomes barrel-shaped as Y' = 3.75. Then, the image of the barrel-shaped effective imaging area of the short focal end is converted into rectangular image information with reduced distortion by image processing.

Accordingly, values corresponding to conditional expressions (1) to (8) are as in table 4 below, and the following conditional expressions (1) to (8) are satisfied.

[ Table 4]

Fig. 2, 3, and 4 show aberration diagrams of coma aberration, distortion, astigmatism, and spherical aberration at the short focal end, the intermediate focal length, and the far focal end in embodiment 1. In these views, the dashed line in spherical aberration represents the sinusoidal condition, and the solid and dashed lines in astigmatism represent the sagittal (sagittal) and meridional (meridional), respectively. Reference numerals g, d in aberration views of spherical aberration, astigmatism and coma represent g-lines and d-lines, respectively. These are the same as the aberration views in the other embodiment.

[ example 2]

Fig. 5 is a schematic view showing the configuration of an optical system of a zoom lens according to embodiment 2 of the first embodiment of the present invention and a zoom locus from a short focal end (wide angle end) to a long focal end (telephoto end) via a predetermined intermediate focal length; (a) a cross-sectional view along the optical axis of the short focal end (wide angle) is shown; (b) a cross-sectional view along the optical axis showing the focal length between the short focal end and the intermediate focal length (wide-intermediate); (c) a cross-sectional view along the optical axis showing an intermediate focal length (middle); (d) a cross-sectional view along the optical axis showing the focal length between the intermediate focal length and the tele end (intermediate-far focus); (e) a cross-sectional view along the optical axis of the tele end (afocal) is shown. In fig. 5 showing the lens group configuration in embodiment 2, the left side of the figure is the object side.

The zoom lens shown in fig. 5 includes, in order along the optical axis from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and an aperture stop AD between the second lens group G2 and the third lens group G3. The first lens group G1 includes a first lens L11, a second lens L12, and a third lens L13. The second lens group G2 includes a first lens L21, a second lens L22, and a third lens L23. The third lens group G3 includes a first lens L31, a second lens L32, and a third lens L33. The fourth lens group G4 includes a single lens L40.

The first-fourth lens groups G1-G4 are supported by a support frame common to each of the lens groups, respectively, and work together for each lens group upon zooming. The aperture stop AD works independently of each group. In fig. 5, the surface number of each optical surface is shown. In addition, reference numerals in fig. 5 are used for each embodiment to avoid complicating the description due to the increase in the number of the reference numerals. For this reason, in the case where reference numerals common to numerals in the drawings of the other embodiment are applied, these are not always configurations common to the other embodiment.

When changing magnification from the short focal end to the long focal end, all of the first-fourth lens groups G1-G4 are moved so that the interval between the first lens group G1 and the second lens group G2 increases, the interval between the second lens group G2 and the third lens group G3 decreases, the interval between the third lens group G3 and the fourth lens group G4 increases, and the first lens group G1 and the third lens group G3 are moved to be positioned closer to the object side at the long focal end than at the short focal end.

The first lens group G1 includes, in order from the object side, a first lens (negative lens) L11 of a negative meniscus lens having a convex surface on the object side, a second lens (first positive lens) L12 of a positive meniscus lens having a convex surface on the object side, and a third lens (third positive lens) L13 of a positive meniscus lens having a convex surface on the object side. The two lenses of the first lens L11 and the second lens L12 are closely attached to each other to form a cemented lens having two lenses.

The aperture stop AD is disposed between the second lens group G2 and the third lens group G3.

The third lens group G3 includes, in order from the object side: a first lens (first positive lens) L31 which is a biconvex positive lens having a strong convex surface on the object side and an aspherical lens forming aspherical surfaces on both surfaces; a second lens (second positive lens) L32 of a double convex positive lens having a strong convex surface on the object side; and a third lens (negative lens) L33 of a double concave negative lens having a strong concave surface on the image side. The two lenses of the second lens L32 and the third lens L33 are closely attached to each other to form a cemented lens of the two lenses.

The fourth lens group G4 includes a single positive lens L40, and the lens L40 is a positive meniscus lens having a convex surface on the object side and an aspherical lens having an aspherical surface on the object side.

In this case, as shown in fig. 5, when changing the magnification from the short focal end (wide angle end) to the long focal end (telephoto end), the first lens group G1 monotonously moves from the image side to the object side, the second lens group G2 moves to the image side to draw a convex locus, and the third lens group G3 moves from the image side to the object side, from the object side to the image side, and again from the image side to the object side, the fourth lens group G4 moves to the object side to draw a convex locus.

The optical characteristics of each optical element in example 2 are shown in table 5 below.

[ Table 5]

In table 5, "+" indicates a non-spherical surface, "HOYA" and "OHARA" indicate the names of glass manufacturers HOYA inc. This is the same in another embodiment.

That is, in table 5, each of the sixth, tenth, twelfth, thirteenth, and seventeenth surfaces to which ". sup." is applied is an aspherical surface, and the parameters of each of the aspherical surfaces in equation 1 are as shown in table 6 below.

[ Table 6]

Coefficient of non-spherical surface

	K	A4	A6	A8	A10
						6	0	-1.55548E-04	3.71202E-06	-5.52669E-08	4.22128E-10
10	0	-5.18794E-04	1.81659E-06	-5.38944E-07	-1.2313E-08
						12	0	-6.41712E-04	2.82143E-05	-2.79043E-06	1.16780E-07
13	0	1.75023E-04	3.95581E-05	-3.73008E-06	1.51988E-07
						17	0	-1.64923E-05	3.14180E-07	8.55118E-08	-1.87844E-09

In embodiment 2, as zooming proceeds, the focal length F, the F value F, the half aperture angle ω, the variation interval DA between the first and second lens groups G1, G2, the variation interval DB between the second lens group G2 and the aperture stop AD, the variation interval DC between the aperture stop AD and the third lens group G3, the variation interval DD between the third and fourth lens groups G3, G4, the variation interval DE between the fourth lens group G4 and the filter FM, and the like of the entire optical system are changed as shown in table 7 below.

[ Table 7]

The aperture diameter of the aperture stop AD at the telephoto (far focus) end isThe image height Y' = 4.1. Referring to fig. 20, as described above, in order to correct distortion by image processing, the imaging region of the long focus end (intermediate focal length) substantially conforms to the imaging region of the light receiving element to obtain a rectangular imaging region, and distortion is generated at the short focus (wide angle) end so that the imaging region of the short focus end becomes barrel-shaped as Y' = 3.75. Then, the image of the barrel-shaped effective imaging area of the short focal end is converted into rectangular image information with reduced distortion by image processing.

Accordingly, values corresponding to conditional expressions (1) to (8) are as shown in table 8 below, and the following conditional expressions (1) to (8) are satisfied.

[ Table 8]

Fig. 6, 7, 8 show aberration diagrams of coma aberration, distortion, astigmatism and spherical aberration at the wide angle end, the intermediate focal length and the far focus end in embodiment 2. In these views, the dashed line in spherical aberration represents the sinusoidal condition, and the solid and dashed lines in astigmatism represent the sagittal and meridional, respectively. Reference numerals g, d in aberration views of spherical aberration, astigmatism and coma represent g-lines and d-lines, respectively. These are the same as the aberration views in the other embodiment.

[ example 3]

Fig. 9 is a schematic view showing the configuration of an optical system of a zoom lens according to embodiment 3 of the first embodiment of the present invention and a zoom locus from a short focal end (wide angle end) to a long focal end (telephoto end) via a predetermined intermediate focal length; (a) a cross-sectional view along the optical axis of the short focal end (wide angle) is shown; (b) a cross-sectional view along the optical axis showing focus between the short focal end and the intermediate focal length (wide-intermediate); (c) a cross-sectional view along the optical axis showing an intermediate focal length (middle); (d) a cross-sectional view along the optical axis showing the focal distance between the intermediate focal length and the tele end (intermediate-far focus); (e) a cross-sectional view along the optical axis of the tele end (afocal) is shown. In fig. 9 showing the lens group configuration of embodiment 3, the left side of the figure is the object side.

The zoom lens shown in fig. 9 includes, in order along the optical axis from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and an aperture stop AD between the second lens group G2 and the third lens group G3. The first lens group includes a first lens L11, a second lens L12, and a third lens L13. The second lens group G2 includes a first lens L21, a second lens L22, and a third lens L23. The third lens group G3 includes a first lens L31, a second lens L32, and a third lens L33. The fourth lens group G4 includes a single lens L40.

The first lens group G1 includes, in order from the object side, a first lens (negative lens) L11 of a negative meniscus lens having a convex surface on the object side, a second lens (first positive lens) L12 of a positive meniscus lens having a convex surface on the object side, and a third lens (second positive lens) L13 of a positive meniscus lens having a convex surface on the object side. The two lenses of the first lens L11 and the second lens L12 are closely attached to each other to form a cemented lens having two lenses.

In this case, as shown in fig. 9, when changing the magnification from the short focal end (wide angle end) to the long focal end (telephoto end), the first lens group G1 monotonously moves from the image side to the object side, the second lens group G2 moves to the image side to draw a convex locus, the third lens group G3 moves from the image side to the object side, moves from the object side to the image side, and moves again from the image side to the object side, and the fourth lens group G4 moves to the object side to draw a convex locus.

The optical characteristics of each optical element in example 3 are shown in table 9 below.

In table 9, "+" denotes a non-spherical surface, "HOYA" and "OHARA" denote the names of glass manufacturers HOYA inc. This is the same in another embodiment.

That is, in table 9, each of the sixth, tenth, twelfth, thirteenth, and seventeenth surfaces to which ". sup." is applied is an aspherical surface, and the parameters of each of the aspherical surfaces in equation 1 are shown in table 10 below.

[ Table 10]

Coefficient of non-spherical surface

	K	A4	A6	A8	A10
						6	0	-2.01225E-07	3.03676E-06	-9.28013E-08	8.85457E-10
10	0	-4.71631E-04	1.31394E-06	-4.32224E-07	-3.24959E-08
						12	0	-7.00887E-04	3.06337E-05	-2.76257E-06	1.25320E-07
53	0	1.92836E-04	4.13616E-05	-3.68036E-06	1.65944E-07
						17	0	-9.81990E-05	3.85346E-06	-8.48706E-08	7.29562E-10

In embodiment 3, with zooming, the focal length F, the F value F, the half aperture angle ω, the variation interval DA between the first and second lens groups G1, G2, the variation interval DB between the second lens group G2 and the aperture stop AD, the variation interval DC between the aperture stop AD and the third lens group G3, the variation interval DD between the third and fourth lens groups G3, G4, the variation interval DE between the fourth lens group G4 and the filter FM, and the like of the entire optical system are 2 changed as shown in table 11 below.

[ Table 11]

The aperture stop at the tele end has an opening diameter ofThe figure showsLike height Y' = 4.1. Referring to fig. 20, as described above, in order to correct distortion by image processing, the imaging region of the long focus end (intermediate focal length) substantially coincides with the imaging region of the light receiving element to obtain a rectangular imaging region, distortion is generated at the short focus (wide angle) end so that the imaging region of the short focus end becomes barrel-shaped as Y' = 3.85. Then, the image of the barrel-shaped effective imaging area of the short focal end is converted into rectangular image information with reduced distortion by image processing.

Accordingly, values corresponding to the conditional expressions (1) to (8) are as shown in the following table 12, and the following conditional expressions (1) to (8) are satisfied.

[ Table 12]

Fig. 10, 11, 12 show aberration diagrams of coma aberration, distortion, astigmatism and spherical aberration at the wide angle end, the intermediate focal length and the far focus end in embodiment 3. In these views, the dashed line in spherical aberration represents the sinusoidal condition, and the solid and dashed lines in astigmatism represent the sagittal and meridional, respectively. Reference numerals g, d in aberration views of spherical aberration, astigmatism and coma represent g-lines and d-lines, respectively. These are the same as the aberration views in the other embodiment.

[ example 4]

Fig. 13 is a schematic view showing the configuration of an optical system of a zoom lens according to embodiment 4 of the first embodiment of the present invention and a zoom locus from a short focal end (wide angle end) to a long focal end (telephoto end) via a predetermined intermediate focal length; (a) a cross-sectional view along the optical axis of the short focal end (wide angle) is shown; (b) a cross-sectional view along the optical axis showing the focal length between the short focal end and the intermediate focal length (wide-intermediate); (c) a cross-sectional view along the optical axis showing an intermediate focal length (middle); (d) a cross-sectional view along the optical axis showing the focal length between the intermediate focal length and the tele end (intermediate-far focus); (e) a cross-sectional view along the optical axis of the tele end (afocal) is shown.

The zoom lens shown in fig. 13 includes, in order along the optical axis from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and an aperture stop AD between the second lens group G2 and the third lens group G3. The first lens group G1 includes a first lens L11, a second lens L12, and a third lens L13. The second lens group G2 includes a first lens L21, a second lens L22, and a third lens L23. The third lens group G3 includes a first lens L31, a second lens L32, and a third lens L33. The fourth lens group G4 includes a single lens L40.

The third lens group G3 includes, in order from the object side: a first lens (first positive lens) L31 which is a biconvex positive lens having a strong convex surface on the object side and an aspherical lens forming aspherical surfaces on both surfaces; the second lens (second positive lens) L32 has a biconvex positive lens having a strong convex surface on the object side; and a third lens (negative lens) L33 of a double concave negative lens having a strong concave surface on the image side. The two lenses of the second lens L32 and the third lens L33 are closely attached to each other to form a cemented lens of the two lenses.

In this case, as shown in fig. 13, when changing the magnification from the short focal end (wide angle end) to the long focal end (telephoto end), the first lens group G1 monotonously moves from the image side to the object side, the second lens group G2 moves to the image side to draw a convex locus, and the third lens group G3 moves from the image side to the object side, from the object side to the image side, and again from the image side to the object side, the fourth lens group G4 moves to the object side to draw a convex locus.

The optical characteristics of each optical element in example 4 are shown in table 13 below.

[ Table 13]

In table 13, "+" indicates an aspherical surface, "HOYA" and "OHARA" indicate the names of glass manufacturers HOYA inc. This is the same in another embodiment.

That is, in table 13, each of the sixth, tenth, twelfth, thirteenth, and seventeenth surfaces to which "") is applied is an aspherical surface, and the parameters of each aspherical surface in equation (9) are shown in table 14 below.

[ Table 14]

Coefficient of non-spherical surface

	K	A4	A6	A8	A10
						6	0	-2.13100E-04	5.36880E-06	-1.07091E-08	-8.91080E-10
10	0	-6.87197E-04	-8.009007E-06	7.90956E-07	-9.47677E-08
						12	0	-6.68388E-04	2.76877E-05	-2.52557E-06	1.10843E-07
13	0	1.82600E-04	3.92416E-05	-358749E-06	1.52005E-07
						17	0	-2.42568E-05	3.24165E-06	-1.12435E-07	1.76648E-09

In embodiment 4, as zooming proceeds, the focal length F, the F value F, the half aperture angle ω, the variation interval DA between the first and second lens groups G1, G2, the variation interval DB between the second lens group G2 and the aperture stop AD, the variation interval DC between the aperture stop AD and the third lens group G3, the variation interval DD between the third and fourth lens groups G3, G4, the variation interval DE between the fourth lens group G4 and the filter FM, and the like of the entire optical system are changed as shown in table 15 below.

[ Table 15]

The aperture diameter of the aperture stop AD at the telephoto (far focus) end isThe image height Y' = 4.1. Referring to fig. 20, as described above, in order to correct distortion by image processing, the imaging region of the long focus end (intermediate focal length) substantially conforms to the imaging region of the light receiving element to obtain a rectangular imaging region, and distortion is generated at the short focus (wide angle) end so that the imaging region of the short focus end becomes barrel-shaped as Y' = 3.65. Then, the image of the barrel-shaped effective imaging area of the short focal end is converted into rectangular image information with reduced distortion by image processing.

Accordingly, values corresponding to the conditional expressions (1) to (8) are as shown in the following table 16, and the following conditional expressions (1) to (8) are satisfied.

[ Table 16]

Fig. 14, 15, 16 show aberration diagrams of coma aberration, distortion, astigmatism and spherical aberration at the wide angle end, the intermediate focal length and the far focus end in embodiment 4. In these views, the dashed line in spherical aberration represents the sinusoidal condition, and the solid and dashed lines in astigmatism represent the sagittal and meridional, respectively. Reference numerals g, d in aberration views of spherical aberration, astigmatism and coma represent g-lines and d-lines, respectively. These are the same as the aberration views in the other embodiment.

As described above, according to embodiments 1 to 4 of the first embodiment of the present invention, it is possible to provide a zoom lens having a sufficiently wide angle, that is, having a half-field angle of 38 degrees or more at the short focal end and a magnification of 8 times or more. The zoom lens also realizes a small size with a configuration of about 10 lenses and a resolution corresponding to an imaging element having 1 million to 1 thousand 5 million pixels for the entire magnification range. According to the second embodiment of the present invention, by using the zoom lens according to the first embodiment of the present invention, a small and high-quality imaging apparatus such as a digital camera including an enlarged range that well covers a general-purpose photographing area can be realized, and an information apparatus such as a portable digital assistant including the imaging apparatus can be realized.

Further, by well correcting the off-axis aberration of the short focal end, a high-performance and small zoom lens can be provided, and by using such a zoom lens, a small imaging apparatus and a small information apparatus that obtain a good photograph at the peripheral portion of the screen of the short focal end can be realized.

Further, by further correcting each aberration well, a stable zoom lens with high performance can be provided, and a high-quality imaging apparatus and an information apparatus with high resolution can be realized.

Although the embodiments of the present invention are described below, the present invention is not limited thereto. It will be appreciated by those skilled in the art that changes could be made in the embodiments described without departing from the scope of the invention.

Claims

1. A zoom lens includes, in order from an object side:

a first lens group having a positive refractive power;

a second lens group having a negative refractive power, the second lens group including, in order from an object side, a first negative lens, and a cemented lens including a second negative lens having a convex shape on the object side and a positive lens;

a third lens group having positive refractive power;

a fourth lens group having positive refractive power; and

an aperture stop disposed between the second lens group and the third lens group,

when changing magnification from a short focal end to a far focal end, an interval between the first lens group and the second lens group increases, an interval between the second lens group and the third lens group decreases, an interval between the third lens group and the fourth lens group increases, and the first lens group and the third lens group are moved to be positioned closer to the object side than the short focal end at the long focal end,

characterized in that the following conditional expression is satisfied, in which an interval between the second lens group and the aperture stop at the short focal end is D2Sw, and an interval between the aperture stop at the short focal end and the third lens group is DS3 w;

0.3＜DS3w/D2Sw＜2.0。

2. the zoom lens according to claim 1, wherein the following conditional expression is satisfied, wherein a focal length of the first negative lens of the second lens group is f21, and a focal length of the second negative lens of the second lens group is f 22;

0.1＜f21/f22＜0.8。

3. the zoom lens according to claim 1, wherein the following conditional expression is satisfied, wherein a focal length of the first negative lens of the second lens group is f21, and a focal length of the second lens group is f 2;

0.5＜f21/f2＜1.5。

4. the zoom lens according to claim 1, wherein the following conditional expression is satisfied, wherein a thickness of the second lens group on the optical axis is D2, and a focal length of the entire lens system at the short focal end is fw;

0.7＜D2/fw＜1.3。

5. the zoom lens according to claim 1, wherein the positive lens of the second lens group is a positive meniscus lens having a convex surface on the object side and an aspherical lens forming an aspherical surface on the image side.

6. The zoom lens according to claim 1, wherein the following conditional expression is satisfied, wherein a variation in an interval between the first lens group and the second lens group when changing magnification from a short focal end to a long focal end is X1-2, and a focal length of the second lens group is f 2;

2.0＜|X1-2/f2|＜4.0。

7. the zoom lens according to claim 1, wherein the following conditional expression is satisfied, wherein an effective beam diameter of an object-side surface of the first negative lens of the second lens group isAnd the effective beam diameter of the object side surface of the second negative lens of the second lens group is

8. An imaging apparatus characterized by comprising the zoom lens according to claim 1 as an imaging optical system.

9. An information apparatus characterized by comprising the zoom lens according to claim 1 as an imaging optical system.